can some one please help. my 318is has lost all its power and it is using loads of petrol it idles between 500 + 2500 revs the o2 sensor is stuck on high the garage told me but they say that it would not make it do all of the things it is doing can any one help?

in most cases when the motor is cold an you drive with low rpm the motor runs good. if he goes warmer, you run with higher rpm and the motor runs retty shit it's a damage in your ignition coils (resitance runs up caused of increased temperature-> igniton voltage goes down)